In construction, a firewall is created from special slow-burning material and is used to slow the advance of a fire. On a computer with an Internet connection, a firewall is designed to restrict Internet access, primarily to keep unwanted guests from getting in. The firewall effectively plugs holes left open when the Internet was originally designed. Windows comes with Windows Firewall. You start it from the Control Panel: Click the heading System and Security, and then click the heading Windows Firewall.As far as you’re concerned, Windows Firewall has only two settings: On and Off. To change the setting, click the link Turn Windows Firewall On or Off on the left side of the Windows Firewall window.When the firewall detects unwanted access, either to or from the Internet, you see a pop-up window office 2010 professional alerting you to the intrusion. At that point, you can choose to allow access by the named program by clicking the Allow Access button. If you want to continue blocking the program, just click Cancel.Windows Defender.Windows Defender is a single name given to a slate of tools used to protect your PC from snooping programs as well as from irritating startup programs. At its core, however, Windows Defender scans your PC for nasty programs known as spyware.In Windows 7, the Windows Defender program runs automatically. To specifically visit the Windows Defender program window, follow these steps:1. Click the Start button.2. In the Search box at the bottom of the menu, type Windows Defender.3. Choose Windows Defender from the search results list that’s displayed. Just press the Enter key to open the window. The Windows Defender main window is rather boring — unless you have a problem. Otherwise, it just lists a quick summary saying that your PC is running normally.